电网设备线夹开裂原因

某电力公司变电站用铝合金设备线夹在运行过程发生批次开裂事故,通过宏观观察、断口分析、化学成分分析、力学性能测试、冷冻模拟试验等方法,对设备线夹的开裂原因和开裂机理进行了分析。结果表明:设备线夹焊缝存在焊接缺陷,导致焊缝强度下降;设备线夹接线管底部存在积水空间,寒冷天气下积水结冰,体积膨胀,使焊缝承受设计工况外的负载而过载开裂,造成了线夹开裂。     

高纯度磷脂酰肌醇的提取工艺研究

以低磷脂酰胆碱(PC)含量大豆粉末磷脂为原料,建立以碱性乙醇为溶剂结合冷冻纯化制备高纯度磷脂酰肌醇(PI)的方法。在单因素实验的基础上利用响应面优化实验确定PI的最佳提取条件为:冷冻时间17 h,冷冻温度-20℃,提取温度40℃,料液比1∶27,98%乙醇与25%氨水体积比100∶4,提取时间40 min,提取次数3次。在最佳条件下,产物PI含量为82.62%,得率为14.29%。     

复合护色剂预处理及不同冻融条件对冷冻双孢蘑菇品质的影响

本实验针对冷冻双孢蘑菇在冻融过程中的品质劣变问题,研究了柠檬酸、L-半胱氨酸、抗坏血酸、异抗坏血酸钠等护色剂对双孢蘑菇褐变的影响,进一步分析了不同冷冻温度(-80、-40、-20℃)和解冻温度(25、4℃)对双孢蘑菇的汁液流失率、质构特征、微观结构、水分含量与分布及过氧化物酶活力等指标的影响。结果表明,复合护色剂配比为3.0 g/L异抗坏血酸钠、1.5 g/L L-半胱氨酸、0.4 g/L抗坏血酸、10 g/L柠檬酸时具有最佳护色效果;-80℃冷冻、4℃解冻的冻融条件下,双孢蘑菇汁液流失率为1.98%,显著低于其他各处理组;水分含量、质构特征值均高于其他冻融条件处理的双孢蘑菇;因此,-80℃冷冻、4℃解冻的冻融条件是较合理的冻融处理方式。本研究为冷冻双孢蘑菇产品的开发及冻融技术提供了参考。     

中国对虾超声辅助解冻的数值模拟及对蛋白变性的影响

为探究中国对虾超声辅助解冻过程中温度分布和解冻时间的变化规律以及对蛋白变性的影响,采用有限元分析软件COMSOL对超声辅助解冻非稳态过程进行模拟并验证,同时测定解冻后肌原纤维蛋白结构与肌肉热稳定性的变化,旨在建立中国对虾的超声辅助解冻模型,为其解冻工艺的确定提供参考。结果表明:超声辅助解冻时中国对虾中心温度模拟值和实验值的均方根误差(root mean square error,RMSE)为0.943 3℃,静水解冻处理组的RMSE为0.907 7℃,证明该模型能较好地模拟解冻过程;与静水解冻相比,超声辅助解冻的解冻时间缩短了35.9%,显著提高了解冻速率;解冻后肌球蛋白重链和肌动蛋白没有发生变化,分子质量为70～100 kDa蛋白片段发生一定程度的降解和交联;最大荧光吸收波长无显著变化,但荧光强度增加;超声辅助解冻后肌肉的热稳定性接近鲜样,而静水解冻后肌肉热稳定性变差。综上认为超声辅助解冻是一种高效且有利于保持冷冻中国对虾品质的解冻方法。     

The effect of gelation on statically and dynamically freeze-cast structures

Freeze-casting is a technique used to produce structures with anisotropic porosity in the form of well-defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La_0.66Ca_0.26Sr_0.07 Mn_1.05O₃. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze-casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non-gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB^®.     

超声波解冻与传统解冻方式的比较与竞争力评估

超声波解冻通过空化效应、机械效应和热效应对冷冻食品进行解冻,解冻效率高、对冷冻食品的损伤较小。该文简要介绍了空气解冻、水解冻和电解冻的解冻机制及研究进展,详细阐述了超声波解冻的机制及研究进展。将超声波解冻与空气解冻、水解冻和电解冻进行对比,发现超声波解冻的解冻效率最优,且将超声波与这3种传统解冻方式结合可以提高解冻效率,并且获得更好的解冻效果。超声波频率和强度以及冻结食品的解冻温度是影响解冻效果的主要参数。超声波在食品中的衰减程度受到解冻温度的影响极大,因此在调节超声波频率和强度同时调控解冻温度对解冻效果至关重要。     

Study of key parameters in modeling liquid hydrogen release and dispersion in open environment

Hydrogen storage in liquid state is considered key feature to its efficient volumetric density for transportation applications. However, there are several hazards associated with handling liquid hydrogen, e.g. fire, explosion, asphyxiation in indoor accidents, and frostbites due to exposure in extremely low temperatures. Predictive capabilities of liquid hydrogen dispersion are essential for developing emergency response plans and facilitate the understanding of the physical problem. In the present study, the Computational Fluid Dynamics (CFD) methodology is employed to simulate the dispersion of liquid hydrogen based on experiment conducted by the Health Safety Laboratory (HSL), in order to investigate several factors that greatly influence dispersion modeling. The flashed vapour fraction at the pipe exit is estimated assuming isenthalpic expansion combined with the NIST equation of state. Modeling the condensation of ambient humidity and air components (nitrogen and oxygen) and imposing transient wind profile are the main issues addressed by the present study. The Homogeneous Equilibrium Model (HEM model) is compared against the Non-Homogeneous Equilibrium Model (NHEM model) to account for slip effects of the non-vapour phase. To estimate the slip velocity in the NHEM model a methodology (momentum slip model) is employed, which solves along with the conservation equations for the mixture the momentum conservation equation of the non-vapour phase. Comparison of the momentum slip model with the algebraic slip model shows that the latter overestimates the slip velocity for large particles and thus its use needs special attention. Overall satisfactory agreement was found with the experimental data when all the above parameters were modelled.     

超声辅助冷冻技术的作用机制及其对食品品质影响的研究进展

冷冻是一种重要的食品保藏技术,但冻结也会引起食品品质的变化。作为一项高新加工技术,超声辅助冷冻技术可以加快冷冻速率,减小冰晶的尺寸,进而改善冷冻食品的品质。本文主要论述了超声辅助冷冻技术的作用机制及对冰结晶形成的影响,同时综述了超声辅助冷冻技术对食品品质的影响及食品冷冻中常用的工艺参数。最后,展望了超声辅助冷冻技术的发展方向,为超声辅助冷冻技术在食品中的应用提供理论支持。